perl allow two forms to create objects:
So you module must allow too:
my $obj1 = new_ok( 'Some::Class' =>  );
my $obj2 = new_ok( $obj1 =>  );
That's a simple enough patch to new_ok, it just needs to get the class name
from the object before passing it to isa_ok. Would you like to write it up
yourself? Tests are in t/new_ok.t.
Closing as wontfix. someone can reopen if this is actually something enough people want.